With constant development of display technology, the requirement for driving ability of a liquid crystal display (LCD) module driving circuit is more and more urgent, and more and more flexible printed circuits (FPCs) will be provided with a quad flat no-lead packaged (QFN) direct current to direct current (DC-DC) device.
However, since the DC-DC driving circuit has many subsidiary circuits which are distributed intensively, it is difficult to leave a detecting point on the FPC due to the limitation of the wiring space on the FPC, in addition to factors, such as less pitch of the QFN device, and limitations of process and procedure of surface mounted technology (SMT) of domestic-made FPC, the DC-DC device and the subsidiary circuit have undesirable conditions such as empty soldering and short circuit. In the conventional detecting method, the soldering state is determined and thus the faulty soldering is detected only by observing or automatic optic inspection (AOI) and detecting input/output resistance state of the FPC. However, in the conventional electrical detecting method, the input/output resistance state is detected when the whole FPC is not powered on, the soldering state of the subsidiary circuit of the DC-DC device can not be detected correctly, especially for the QFN devices, which have no leakage pin and thus on which manual electrical detection can not be performed.